Magnetic starter with long time delay



D 1941- w. SCHAELCHLIN 2,265,009

MAGNETIC STARTER WITH LONG TIME DELAY Filed Jan. 24, 1940 WITNESSES: INVENTOR ATTORNEY Patented Dec. 2, 1941 UNITED STATES PATENT OFFICE Walter Schaelchlin, Wilkinsburg, Pa., assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application January 24, 1940, Serial No. 315,351

13 Claims. (01. 172288) My invention relates to an electric control system which embodies a time-limit relay of the flux decay type, more specifically a time-limit relay having a neutralizing coil for regulating the flux decay, which neutralizing coil is intermittently energized in order to prolong the total period of time delay of the relay.

An object of my invention is to provide a control system for starting an electric motor, which control system includes magnetic time element relays having an unusually large time constant.

Another object of my invention is to provide a time element relay of the flux decay type with a time constant which is much greater than similar devices used in the prior art and which includes an intermittently energized neutralizing coil for allowing flux decay step by step thereby prolonging the total time delay of the relay.

Other objects and advantages will become more apparent from a study of the following specification when considered in conjunction with the accompanying drawing, in which:

Figure l is a schematic showing of a control system embodying the principles of my inven tion;

Fig. 2 is a curve showing a flux decay characteristic of a time delay relay operated in accordance with the principles of my invention.

Referring more particularly to Figure 1, numeral l denotes the armature of an electric motor M and numerals 2 and 3 denote, respectively, the series and shunt fields of the motor to be controlled. A variable resistor 4 is connected in series with the shunt field 3 and a series resistor 5 is connected in series with the armature l and series field winding 2, respectively. Successive portions of a series resistor 5 may be shunted by means of the accelerating contactors 6, l, 8 and 9, all of which accelerating contactors are of the time delay type and are substantially identical to those described in my former Patent No. 1,979,709, (i. e. in which I am a co-inventer) issued November 6, 1934, entitled Time limit contactor, and in my former Patent No. 1,994,925, issued March 19, 1935, entitled Inductive time limit acceleration. The outstanding difference between my present timelimit relay and the former relays is in the connection of the neutralizing coils to the system. More specifically, I have provided an intermittently operated time element relay In which effects intermittent energization of the neutralizing coils ll, I2, l3 and I4, thereby prolonging the time delay of each of the accelerating cona greater period, say, ten to fifteen seconds, or, in fact, a period of indefinite length.

Many instances arise in practice where such long periods in the successive accelerating steps for starting a motor are required, particularly in the case of a very large motor having very large inertia and requiring a long period of time to come up to a predetermined speed. It is to this latter type of equipment that my invention is particularly adapted.

My invention will best be understood by outlining the operation of the device which is as follows: Assume that the motor M is at rest and the control system is in a deenergized condition such as shown in Fig. 1. Assume now that the start pushbutton I5 is depressed thereby completing a circuit from a positive bus I6 of a suitable direct current source of potential through contact members of the start pushbutton I5, contact members ll, conductor 18, actuating coil I9, conductor 20 to the negative busterminal 2|. Energization of actuating coil l9 will operate relay 6 in a manner to effect closing of contact members 22 and 23 which, in turn, complete energizing circuits for actuating coils 24 and 25 of contactors I and 8, respectively, causing these contactors to operate. Operation of contactors l and 8 will effect closing of their respective contact members 26 and 21 which, in turn, complete energizing circuits through actuating coils 28 and 29 of contactors 9 and ill, respectively.

The energizing circuit through actuating coil 28 may be traced from positive bus terminal l6 through start pushbutton I5, conductor 32, contact members 22 and 23, conductor 33 and contact members 26, conductor 30, actuating coil 28, conductor 3| to the negative bus terminal 2|. The energizing circuit for actuating coil 29 is traced in the same manner up to and through conductor 30, thence going through a parallel path including contact members 21, conductors 34 and 62, contact members 35, actuating coil 29, conductor '36 to the negative bus terminal 2!.

Thus, all of the accelerating contactors 6 to 9, inclusive, together with the time element contactor [0, are immediately energized following depression of the start pushbutton [5 with the resultant effect that their respective contact members 31, 38, 39, 40 and 35 are opened.

By the closure of contact members 43 on contactor 9 a still further energizing circuit is completed through actuating coil 4| of line contactor 42 which circuit may be traced similarly to the circuit traced above through actuating coil 29 tactors from a period of roughly five seconds to except that the present circuit branches off from conductor 34 to contact members 43, conductors 44 and 45, actuating coil 4|, conductor 46 to the negative bus terminal. Thus, line contactor 42 is energized thereby effecting closing of its con-- tact members 41 and 48 and the opening of contact members IT. The opening of contact members 31 to 40, inclusive, places all sections of the series resistor 5 in series with armature I of the motor so long as contact members 41 remain closed. Such contact members 41 remain closed by virtue of a holding circuit which may be traced from the positive bus terminal I6 through conductor 59, stop pushbutton 49, contact members 48, conductor 45, actuating coil 4 I, conductor 46 to the negative bus terminal 2|, and which circuit remains throughout the entire operation of the motor. Depression of the stop pushbutton 49 only will effect deenergization of actuating coil 4|. Now although the start pushbutton I5 has been released, there still remains an energizing circuit for coils 24, 25, 28 and 29 which may be traced from the positive bus terminal I6 to conductor 50, stop pushbutton 49, contact members 48, conductor 44, contact member 43, conductor 34 (thence through coil 29), contact members 21 (thence through coil 28), conductor 39, contact members 26 (thence through coil 25), conductor 33, contact members 23 (thence through coil 24) to the negative bus terminal 2 I.

Opening of contact members I! will immediately interrupt the circuit through actuating coil I9 oi" contactor 6. However, although the actuating or main coil I9 of contactor 6 is deenergized, the relay will not operate immediately to close the contact members 31 by virtue of the effect of a low-resistance closed coil 5| which is inductively related to coil I9 and the function of which is clearly described in my previous patents hereinabove referred to. Briefly stated, the function of coil 5I is to provide a low resistance path into which a heavy current is induced as a result of deenergization of coil I9 which induced current tends to maintain the flux in the magnetic circuit of the time limit contactor 6.

There is also provided a neutralizing coil II which is wound oppositely to the main coil I9 and whose function is to oppose the magnetic effect of coil I9. Normally the magnetic effect of the neutralizing coil II is quite negligible. However, when the magnetic flux in the magnetic circuit of the time limit contactor has decreased to somewhere near the value of its residual magnetism, the eifect of the neutralizing coil II becomes relatively large and operates to substantially annihilate the residual magnetism at a rate determined by the characteristics of the closed circuit coil 5|.

The neutralizing effect of coil I I may be varied or adjusted by means of the parallelly connected variable resistor 52. Associated with the other contactors I, 8 and 9 are similar variable resistors 53, 54 and 55 for individually adjusting the respective neutralizing coils. Likewise, associated with these other contactors are ringshaped elements 56, 5'! and 58 which are similar in character and purpose as the ring-shaped element 5!. If the neutralizing coil II were permanently connected in the circuit contactor 6 would operate within a definite time interval which interval would be dependent upon the characteristic of the coil 5I, the value of the variable resistor 52 and the tension of spring 59 which is adjusted by a nut or similar adjusting means 60.

In order to prolong the total period of time delay of contactor 6 neutralizing coil II is intermittently energized instead of being permanently energized. The means for effecting such intermittent energization comprises the time element contactor II] which includes a shortcircuited low-resistance ring element 6I similar to element 5| of contactor 6 in that it prevents immediate decay of flux when actuating coil 29 is deenergized. In other words when actuating coil 29 is energized, it will immediately efiect opening of contact members 35. However, when it is deenergized, a current will be induced in ring element 6| which will counteract the flux decay thereby preventing reclosing of contact members 35 for a definite interval of time. As soon as contact members 35 reclose, the circuit will again be established through coil 29 to again effect reopening which circuit may be traced from the positive terminal I6 through conductor 59, stop pushbutton 49, contact members 48, conductor 44, contactmembers 43, conductor 62, contact members 35, actuating coil 29, conductor 36 to the negative bus terminal 2I.

Contact members 35 do not control the energization of the neutralizing windings II, I2, I3 and I4, but the contact members I35, operating in synchronism with the contact members 35, do. The neutralizing windings are thus intermittently energized by the closing and opening of contact members I35.

Referring more particularly to Fig. 2 which shows fluxed plotted against time for each accelerating step and in which the time intervals marked a denote the intervals during which contact members I35 are opened and the intervals 12 denote the intervals of time during which the contact members I35 remain closed, it will be observed that the intermittent periods a of opening of the contact members are of longer duration than the periods b of closing of the contact members I35. This is not absolutely necessary, of course, but is the manner for securing especially long time periods. It will also be observed that the flux decays very rapidly during the periods b of closure of contact members I35, whereas the flux tends to maintain itself during the periods a of opening of the contact members I35. Obviously, the greater the periods a are with respect to periods I) the longer will be the total time for complete decay of the flux, that is, the total time required for any of the relays 6 to 9, inclusive, to operate.

The reason for this is clear. During closed circuit condition of contact members I35, the neutralizing coils II, l2, I3 and I4 are energized thus causing a more rapid decay of flux in their respective magnetic cores, whereas, when contact members I35 are open the neutralizing coils are an open circuit and the decay of flux in the respective cores is much slower.

Now going back and retracing the operation following the deenergization of actuating coil I9 due to opening of contact members I1 and the subsequent shunting (after the lapse of a definite time interval) of a portion of series resistor 5 by closure of contact members 31, it will be observed that the contact member 23 has now opened thereby interrupting the energizing circuit through the next actuating'coil 24. After a predetermined time delay for the operation of contactor 1 similar to that described in connection with contactor 6, contact members 26 open and interrupt the energizing circuit through coil 25, and after contactor 8 has operated contact members 21 will open and interrupt the energizing circuit through coil 28 and finally, when contactor 1 operates, it will open contact members 43 and interrupt the circuit through coil 29 to stop the intermittent operation of relay l0. Contact members 31, 38, 39 and 40 will therefore close in succession, thereby successively shunting more and more of the series resistor 5. As the last portion of series resistor is short circuited by contact members 40, the armature I and series field Winding 2 are thrown directly across the bus terminals I 6 and 2| and thus have the full line voltage applied thereto.

In order to stop the motor, a stop pushbutton 49 is depressed which effects deenergizaticn of actuating coil 4| thereby effecting opening of contact members 4'! and interruption of the main circuit through the armature l and series field winding 2, as well as the auxiliary circuit through actuating coil 4|, thus restoring the control system to the deenergized position such as shown in Fig. 1.

I am, of course, aware that others, particularly after having had the benefit of the teachings of my invention, may devise other devices and systerns of control embodying my invention, and I, therefore, do not Wish to be limited to the specific showings made in the drawing and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims and such prior art that may be pertinent.

I claim as my invention:

1. A time delay magnetic relay system comprising, in combination, a magnetic circuit, coil means for producing a magnetic flux in said z.-

circuit, means inductively related to said coil means for decreasing the rate of decay of said magnetic flux when said coil means for producing the flux is deenergized and means for intermittently energizing said inductively related means.

2. A time delay magnetic relay system comprising, in combination, a magnetic circuit, coil means for producing a magnetic flux in said circuit, means inductively related to said coil means for decreasing the rate of decay of said magnetic flux when said coil means for producing the flux is deenergized and means for intermittently energizing said inductively related means, and means for adjusting the rate of flux decay during said intermittent operation.

3. In an electromagnetic time limit device, in combination, a magnetic circuit, a coil disposed to produce a magnetic flux in said circuit, means inductively related to said coil for decreasing the rate of decay of the magnetic flux in said circuit when the coil is deenergized, and a neutralizing coil disposed to dissipate the residual magnetic flux in said circuit to continue the decay of the flux and means for intermittently energizing said neutralizing coil thereby intermittently effecting appreciable decay of the magnetic flux.

4. In an electromagnetic time limit device, in combination, a magnetic circuit, a coil disposed to produce a magnetic flux in said circuit, a closed circuit inductively related to said coil for decreasing the rate of decay of the magnetic flux in said circuit when the coil is deenergized, and a neutralizing coil disposed to dissipate the residual magnetic fiuX in said circuit to continue the decay of the flux and means for intermittently energizing said neutralizing coil thereby intermittently efiecting appreciable decay of the magnetic flux.

5. In an electromagnetic time-limit device, in combination, a movably mounted armature,

means for biasing the armature to a predetermined position, an electromagnet from which, when deenergized, the lines of magnetic force dissipate rapidly until substantially only the lines of magnetic force constituting the residual magnetism remain, means for decreasing the rate of dissipation of the magnetic force whereby a longer time is required for any given magnetic force to dissipate till only the residual magnetic force remains, and coil means, associated with the electromagnet, adapted to dissipate the residual magnetic force when the electromagnet is deenergized to continue said dissipation of the magnetic force in the electromagnet to eventually permit the operation of the armature under the influence of the biasing means and means for intermittently energizing said coil means.

6. In an electromagnetic time-limit device, in combination, a movably mounted armature, adjustable means for adjustably biasing the armature to a predetermined position, an electromagnet from which, when deenergized, the magnetic flux decays at a rapid rate until substantially only the residual magnetic flux remains, said electromagnet, when energized, being adapted to actuate said armature against said biasing means, adjustable and intermittently operated control means for dissipating the residual magnetic flux of the electromagnet to selectively increase the time by a substantially predetermined amount during which the flux decays at a rapid rate, and means for decreasing the rate of the rapid decay to further lengthen the time during which the magnetic flux decays, thereby increasing the time during which the positive functioning of the armature may be obtained in response to the force of said biasing means.

7. In an electromagnetic time-limit device, in combination, a core member, an armature, a spring for biasing the armature to a predetermined position, a coil for magnetizing the core member to effect the operation of the armature, control means for decreasing the rate of dissipation of the magnetic flux in the core member when the coil is deenergized, and a neutralizing coil disposed to eifect, when energized, a substantially constant dissipation, at a rate determined by the control means, of the residual magnetism of the core from a maximum energized condition to zero, thereby to obtain a positive action of the armature at any predetermined time during the process of dissipation of the residual magnetism and means for intermittently energizing said neutralizing coil.

2. In an electromagnetic time limit device, in combination, a magnetic circuit, a coil disposed to produce a magnetic flux in said circuit, means inductively related to said coil for decreasing the rate of decay of the magnetic flux in said circuit when the coil is deenergized, and a neutralizing coil disposed to dissipate the residual magnetic flux in said circuit to continue the decay of the flux and means for intermittently energizing said neutralizing coil thereby intermittently effecting appreciable decay of the magnetic flux, said periods of intermittent energization of said neutralizing coil being small compared to the intermittent periods of deenergization of said coil.

9. In an. electromagnetic time-limit device, in combination, a core member, an armature, a spring for biasing the armature to a predetermined position, a coil for magnetizing the core member to effect the operation of the armature, control means for decreasing the rate of dissipation of the magnetic flux in the core member when the coil is deenergized, and a neutraliz ing coil disposed to effect, when energized, a substantially constant dissipation, at a rate determined by the control means, of the residual magnetism of the core from a maximum energized condition to zero, thereby to obtain a positive action of the armature at any predeter mined time during the process of dissipation of the residual magnetism, and means for intermittently energizing said neutralizing coil said periods of intermittent energization of said neutralizing coil being small compared to the intermittent periods of deenergization of said coil.

10. In a system of control for a motor, in combination, a source of energy, a motor, a starting contactor for connecting the motor to the source of energy, a starting resistor therefor, and a plurality of electromagnetic time-limit contactors, comprising means for magnetizing the contactors, intermittent means for intermittently decreasing the rate of decay of the magnetism when said magnetizing means is deenergized and means for causing the decay to continue till there is no residual magnetism left in the contactors, for successively shunting sections of the starting resistor to connect the motor to the full voltage of the source of supply a definite interval of time after the operation of the starting contactor.

11. In a system of control for a motor, in combination, a source of energy, a motor, a starting resistor, an electromagnetic time-limit contactor for shunting said resistor, means for energizing said contactor, a line switch for connecting the motor and starting resistor to the source of energy and for efiecting the deenergization of the energizing means for the time-limit contactor, rate control means for decreasing the rate of decay of the magnetism of the timelimit contactor, and intermittently energized neutralizing control means for intermittently continuing the decay till substantially no residual magnetism remains in the contactor, said time-limit contactor being adapted to shunt said starting resistor when the effect of said rate control means and neutralizing control means has substantially ceased.

12. In a system of control for an electric motor including an accelerating resistor, an electromagnetic time-limit contactor, a source of electrical energy, said contactor having two windings each energized from the source of energy so as to be independent of the operating characteristics of the motor, and a third closed circuit winding inductively related to said firstnamed two windings, one of the first-named windings being disposed to control the closing of the contactor, means for deenergizing the said winding controlling the closing of the contactor, thereby placing the closing of the contactor solely under the control of the other two Windings, and means for intermittently energizing said control winding so as to provide a step by step rapid flux decay, thereby prolonging the total period required for complete decay of the flux.

13. In a system of control for an electric motor including an accelerating resistor, an electromagnetic time-limit contactor, a source of electrical energy, said contactor having two windings each energized from the source of energy so as to be independent of thevoperating characteristics of th motor, and a third closed circuit winding inductively related to said firstnamed two windings, one of the first-named windings being disposed to control the closing of the contactor, means for deenergizing the said winding controlling the closing of the contactor, thereby placing the closing of the contactor solely under the control of the other two Windings, and means for intermittently energizing said control winding so' as to provide a step by step rapid flux decay, thereby prolonging the total period required for complete decay of the flux, said last mentioned means including a time limit device which is effective to intermittently energize said control winding for periods which are comparatively short as compared to the intermittent periods of deenergization thereof.

WALTER SCI-IAELCHLIN. 

